how to convert a shape key animation to a fluid?
Ok now it's clearer. If I got what you mean, I tried a (much simplified and rough) example.

I started from a simple sphere, set basis shape key, 



added another, shaped it like a glass extruding vertices, 



had the morphing effect. 



Then set the morphed glass object as fluid, 



added a surrounding big cube, set it to fluid domain, 



and baked the domain.



When it finished, I hid the original glass shape, keeping only the domain visible. Now it seems to splash as you expect... does it?



Is this not working for you? Did you forget to bake? Of course I used rough fluid settings, you'll need at least much finer domain resolution.